The enzyme, characterized from the bacterium Bacteroides thetaiotaomicron, is part of the biosynthesis pathway of the sialic acid 3-deoxy-D-glycero-D-galacto-non-2-ulopyranosonate (Kdn). Kdn is abundant in extracellular glycoconjugates of lower vertebrates such as fish and amphibians, but is also found in the capsular polysaccharides of bacteria that belong to the Bacteroides genus.